This is not what you are looking for, but amazing enough it is the BEST ring filing tool I've used so far - as far as the 'nothing fancy' classification for a DIY folk goes anyways! lol

So this is a Dino Campolito ring filer, so simple to use and so freaking REPEATABLE!!! All my rings where precisely cut to exactly the dimensions I needed, and produced a very square (ring end to ring end) result once in the bore.

He has a US Patent for this thing, see attachment.